Moulding composition for producing bipolar plates

ABSTRACT

Compositions comprising (a) an epoxy resin, (b) a hardener for the epoxy resin, (c) a product of the reaction of a microgel containing carboxylic acid groups and a nitrogen-containing base, and (d) an electrically conducting filler combination comprising, based on the total amount of filler, at least 75% by weight of graphite, are particularly suitable for producing bipolar plates.

[0001] The present invention relates to epoxy resin compositionscomprising an electrically conducting filler mixture and the use of thiscomposition for producing bipolar plates.

[0002] Moulding compositions with high thermal and electricalconductivity are increasingly gaining importance for specificapplications in the electrical industry, for example in the productionof bipolar plates for fuel cells.

[0003] WO 99/19389 describes hot-curable compositions comprising from 10to 30% by weight of a low-viscosity resin and from 70 to 90% by weightof an electrically conducting filler. The compositions have good thermaland electrical conductivities, and also high cracking resistance.However, these moulding compositions can be produced only in thepresence of solvents and/or using liquid resin-hardener components.

[0004] Mixtures of vinyl ester resins, graphite powder, and, whereappropriate, reinforcing fibres are proposed in WO 00/25372 as compositematerials for producing bipolar plates. In these systems no use ofsolvents if required; however, these products either have insufficientstorage stability for practical use or have a hardening time which istoo long for mass production. When the fuel cell is operating in a hotand humid climate, the unavoidable cleavage of the acid from the esterfunction causes additional problems with catalyst and membrane.

[0005] It was an object of the present invention to providesolvent-free, storage-stable, rapidly curing epoxy resin systems withhigh thermal and electrical conductivity which are capable of productionby an efficient process (extrusion, calendering) in pellet form and,where appropriate, can be processed to give bipolar plates, inparticular by the usual processes for epoxy moulding compositions(injection moulding, transfer moulding, compression moulding).

[0006] The particular challenge here is that an extremely high contentof conducting fillers has to be added to achieve sufficiently goodconductivity in the bipolar plates. At the same time, the fall-off Inflowability of the moulding composition associated with rising fillercontent must not be permitted to restrict processability. Another factorwhich has to be considered here is that the flowability of a thermosetmoulding composition can additionally be reduced prior to introductioninto the final compression mould by any prior exposure to heat (e.g.extrusion, preplastification, residence time in injection mouldingcylinder) due to the onset of the curing reaction. Although this can becounteracted by a general reduction in the curing rate, that would alsoreduce the curing rate at mould temperature. If the bipolar plates areto be capable of useful bulk production with curing times under oneminute, high curing rate at mould temperature is a specific requirement.

[0007] Theoretically, the fall-off in flowability with rising fillercontent could be counteracted by using liquid or very low-viscosityresin components or hardener components, but this advantage isassociated with a considerable series of disadvantages or new problems:

[0008] 1. More difficult handling of the liquid components combined witha problematic homogenization step (homogeneous introduction of solid,insoluble components into liquid components, possible sedimentationproblems) would result in a production process which overall demandsmarkedly more resources in terms of both apparatus and time. Incontrast, solids-only mixtures can be homogenized in commerciallyavailable high-speed mixers within a few seconds. Direct extruderprocessing is then possible. Indeed, in the ideal case the premixingprocess can be omitted entirely, since the solid components can also bemetered directly into the extruder and mixed there.

[0009] 2. As the content of liquid matrix components increases,experience has shown that exudation is to be expected from the matrix toa greater or lesser degree when using conventional compression processesand parameters, e.g. as described in DIN 7708 (“Rieselfähigeduroplastische Formmassen—Herstellung von Probekörpern und Bestimmungder Eigenschaften” [Free-flowing thermoset mouldingcompositions—production of test specimens and determination ofproperties]) or in ASTM D3123-72 (“Spiral Flow of Low-PressureThermosetting Moulding Compounds”) at the appropriate pressures (>69bar) and compression temperatures (150-190° C.). The matrix here isexpelled from the mould itself and the surrounding filler through theparting surface of the mould, and at the parting surface this formsundesirable flash with its known associated disadvantages (increasedadhesion tendency, need for mechanical post-treatment, material loss).At the same time, this loss of matrix causes a fall-off in mechanicalproperties, in extreme cases preventing removal of the moulding from themould. In addition, a low-filler-content matrix layer at the surface ofthe moulding increases the contact resistance between two bipolarplates. On the other hand, lower pressures cause insufficientcompaction, associated with air inclusions, increased shrinkage, andfilling problems during the moulding process.

[0010] 3. When the matrix comprises liquids, latency can generally beexpected to be lower, and storage stability poorer.

[0011] It has now been found that the required property profile can alsobe achieved without the use of liquid matrix components and thedisadvantages associated with these, by simultaneous use of specificmicrogel-amine catalysts and specialized grades of graphite.

[0012] The present invention therefore provides a composition comprising

[0013] (a) an epoxy resin,

[0014] (b) a hardener for the epoxy resin,

[0015] (c) a product of the reaction of a microgel containing carboxylicacid groups and a nitrogen-containing base, and

[0016] (d) an electrically conducting filler combination comprising,based on the total amount of filler, at least 75% by weight of graphite.

[0017] A suitable component (a) for preparing the compositions of theinvention is the usual epoxy resins from epoxy resin technology.Examples of epoxy resins are:

[0018] I) Polyglycidyl and poly(β-methylglycidyl) esters, obtainable byreacting a compound having at least two carboxyl groups in the moleculeand epichlorohydrin or β-methylepichlorohydrin. The reaction usefullytakes place in the presence of bases.

[0019] The compound used having at least two carboxyl groups in themolecule may be an aliphatic polycarboxylic acid. Examples of thesepolycarboxylic acids are oxalic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, and dimerized ortrimerized linoleic acid.

[0020] However, it is also possible to use cycloaliphatic polycarboxylicacids, such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid,hexahydrophthalic acid, or 4-methylhexahydrophthalic acid.

[0021] Aromatic polycarboxylic acids may also be used, for examplephthalic acid, isophthalic acid or terephthalic acid.

[0022] II) Polyglycidyl or poly(β-methylglycidyl) ethers, obtainable byreacting a compound having at least two free alcoholic hydroxy groupsand/or phenolic hydroxy groups with epichlorohydrin orβ-methylepichlorohydrin under alkaline conditions or in the presence ofan acidic catalyst with subsequent treatment with alkali.

[0023] These glycidyl ethers derive from acyclic alcohols, for example,e.g. from ethylene glycol, diethylene glycol or higher polyoxyethyleneglycols, or propane-1,2-diol or polyoxypropylene glycols, orpropane-1,3-diol, butane-1,4-diol, polyoxytetramethylene glycols,pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol,1,1,1-trimethylolpropane, pentaerythritol, or sorbitol, or else frompolyepichlorohydrins.

[0024] Other glycidyl ethers of this type derive from cycloaliphaticalcohols, such as 1,4-cyclohexanedimethanol,bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane,or from alcohols which contain aromatic groups and/or other functionalgroups, for example N,N-bis(2-hydroxyethyl)aniline orp,p′-bis(2-hydroxyethylamino)diphenylmethane.

[0025] The glycidyl ethers may also be based on mononuclear phenols,such as resorcinol or hydroquinone, or on polynuclear phenols, such asbis(4-hydroxyphenyl)methane, 4,4′-dihydroxybiphenyl,bis(4-hydroxyphenyl) sulphone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxyphenyl)propane or2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane. Other hydroxy compoundssuitable for preparing glycidyl ethers are novolaks, obtainable bycondensation of aldehydes, such as formaldehyde, acetaldehyde, chloralor furfuraldehyde, with phenols or bisphenols which are unsubstituted orhave substitution by chlorine atoms or by C₁-C₉-alkyl groups, forexample phenol, 4-chlorophenol, 2-methylphenol, or 4-tertbutylphenol.

[0026] III) Poly(N-glycidyl) compounds, obtainable bydehydrochlorination of the products of the reaction of epichlorohydrinwith amines which contain at least two amine hydrogen atoms. Examples ofthese amines are aniline, n-butylamine, bis(4-aminophenyl)methane,m-xylylenediamine, and bis(4-methylaminophenyl)methane.

[0027] The poly(N-glycidyl) compounds also include triglycidylisocyanurate, N,N′-diglycidyl derivatives of cycloalkyleneureas, such asethyleneurea or 1,3-propyleneure, and diglycidyl derivatives ofhydantoins, for example of 5,5-dimethylhydantoin.

[0028] IV) Poly(S-glycidyl) compounds, such as di-S-glycidyl derivativeswhich derive from dithiols, such as ethane-1,2-dithiol orbis(4-mercaptomethylphenyl) ether.

[0029] V) Cycloaliphatic epoxy resins, such asbis(2,3-epoxycyclopentyl)ether, 2,3-epoxycyclopentyl glycidyl ether,1,2-bis(2,3-epoxycyclopentyloxy)ethane or3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate.

[0030] It is also possible to use epoxy resins in which the 1,2-epoxygroups have been bonded to different heteroatoms or functional groups;examples of these compounds are the N,N,O-triglycidyl derivative of4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid,N-glycidyl-N′-(2-glycidyloxypropyl)-5,5-dimethylhydantoin and2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.

[0031] To prepare the epoxy resin compositions of the invention it ispreferable to use a solid polyglycidyl ether or solid polyglycidylester, in particular a solid diglycidyl bisphenol ether or a soliddiglycidyl ester of a cycloaliphatic or aromatic dicarboxylic acid, or acycloaliphatic epoxy resin. It is also possible to use mixtures of epoxyresins.

[0032] It is preferable to use solid ether-based epoxy resins.

[0033] Solid polyglycidyl ethers which may be used are compounds whosemelting points are from above room temperature to about 250° C. Themelting points of the solid compounds are preferably in the range from50 to 150° C. These solid compounds are known, and some of them areavailable commercially. The advanced products obtained by priorextension of liquid polyglycidyl ethers may also be used as solidpolyglycidyl ethers.

[0034] Particularly preferred components (a) are epoxy phenol novolaksand epoxy cresol novolaks.

[0035] In principle, any of the hardeners known to the person skilled inthe art from epoxy resin technology may be used as component (b).

[0036] Preferred hardeners are phenol novolaks and cresol novolaks.

[0037] The products of the reaction of a microgel containing carboxylicacid groups and a nitrogen-containing base (microgel-amine salts) to beused as component (c) are known from U.S. Pat. No. 5,994,475.

[0038] The microgel in component (c) is preferably a copolymer of atleast one unsaturated carboxylic acid, in particular acrylic acid ormethacrylic acid, and at least one polyfunctional crosslinker.

[0039] To prepare the microgels in component (c) use is preferably madeof a polyfunctional acrylate or methacrylate of an aliphatic,cycloaliphatic or aromatic polyol, an addition product of acrylic acidor methacrylic acid and a polyglycidyl compound, an addition product ofacrylic acid or methacrylic acid and glycidyl acrylate or methacrylate,an alkenyl acrylate or alkenyl methacrylate, a dialkenylcyclohexane, ora dialkenylbenzene as polyfunctional crosslinker.

[0040] Particularly preferred polyfunctional crosslinkers are ethyleneglycol diacrylate, ethylene glycol dimethacrylate, propylene glycoldiacrylate, propylene glycol dimethacrylate, 1,4-butanediol diacrylate,1,4-butanediol dimethacrylate, polyethylene glycol diacrylate,polyethylene glycol dimethacrylate, polypropylene glycol diacrylate,polypropylene glycol dimethacrylate, 1,1,1-trimethylolpropanetriacrylate, 1,1,1-trimethylolpropanetrimethacrylate, bisphenol Adiglycidyl ether diacrylate, bisphenol A diglycidyl etherdimethacrylate, allyl acrylate, allyl methacrylate, divinylcyclohexane,and divinylbenzene.

[0041] The nitrogen-containing base used in preparing component (c) ispreferably an amine, a polyamine or in particular an imidazole.

[0042] Particularly preferred nitrogen-containing bases are2-phenylimidazole, 2-isopropylimidazole, 2-dodecylimidazole,2-heptadecylimidazole, 2-ethylimidazole, and 2-ethyl-4-methylimidazole.

[0043] The electrically conducting filler combination (d) of thecomposition of the invention may be composed of pure graphite or of amixture with other mineral or metallic fillers or carbon blacks, as longas the proportion of the graphite in the entire filler combination (d)is at least 75% by weight, preferably at least 85% by weight,particularly preferably at least 95% by weight.

[0044] The particle diameter of the filler is also significant.

[0045] The graphite powder used has an average particle diameter of from0.1 to 500 μm, more preferably from 1 to 300 μm, particularly preferablyfrom 10 to 250 μm, with particular preference from 50 to 100 μm.Graphite has a layer structure, the electrons flowing along theselayers. When moulded plates are produced, as particle size increasesthese layers become oriented in the plane, so that electricalconductivity in the plane of the plate is greater than across it.

[0046] It is preferable to use synthetic graphite, since it has lessorientation. Unlike natural graphite, it also has only very low levelsof contamination by divalent and trivalent cations which can becomeembedded into the membrane of the fuel cell and thus reduce performance.

[0047] The quantitative proportions of components (a), (b), (c) and (d)in the compositions of the invention may vary within wide ranges.

[0048] The quantitative proportion of epoxy resin (a) to hardener (b) iswithin the conventional ranges known to the person skilled in the art.Preference is given to compositions comprising from 20 to 75% by weightof component (b), based on 100% by weight of component (a).

[0049] The amount of component (c) is from 0.1 to 25% by weight,preferably from 1 to 20% by weight, based on 100% by weight of component(a).

[0050] The amount of filler combination (d) is from 50 to 90% by weight,preferably from 70 to 85% by weight, based on the entire composition ofcomponents (a)+(b)+(c)+(d).

[0051] The compositions of the invention may comprise other conventionaladditives, e.g. anboxidants, light stabilizers, plasticizers, dyes,pigments, agents with thixotropic effect, tougheners, antifoams,antstats, lubricants and mould-release agents. The content of theadditives is included in the filler component (d).

[0052] Surprisingly, the electrical conductivity of the hardened epoxyresin can be considerably increased by adding an organosilane. Examplesof suitable organosilanes are octyltriethoxysilane,methyltriethoxysilane, vinyltriethoxysilane, methyltrimethoxysilane,vinyltrimethoxysilane, γ-aminopropyltrimethoxysilane andγ-glycidyloxypropyltrimethoxysilane.

[0053] The amount of the silane added is preferably from 0.05 to 1% byweight, in particular from 0.1 to 0.5% by weight, based on the entirecomposition.

[0054] As the proportion of graphite in the formulation rises, themechanical properties of the cured resin become poorer. The use offibrous fillers to increase mechanical strength is known from theliterature. However, as described in WO 00/25372, for example, whenfibrous fillers are added it has to be accepted that there will be lossof surface quality, poorer processability of the moulding composition,and the risk of orientation of the fibres, particularly inlarge-surface-area applications, e.g. in the case of bipolar plates. Theproperty profile of the epoxy matrix has been found to be sufficientlygood that even when the proportion of components (a)+(b)+(c) is onlyfrom 15-30% by weight the strengths obtained permit reliable handling ofthe plates during removal from the mould and assembly of the fuel cells.The omission of fibrous fillers permits the moulding of very finestructures with extremely good surface quality.

[0055] The hardening of the epoxy resin compositions of the invention togive mouldings, coatings or the like takes place in the manner usual inepoxy resin technology, as described by way of example in “Handbook ofEpoxy Resins”, 1967, by H. Lee and K. Neville.

[0056] The invention also provides the electrically conductive materialproduced by hardening a composition of the invention.

[0057] The compositions of the invention are suitable as replacementsfor metal in electrical applications and are particularly suitable forproducing bipolar plates for fuel cells.

[0058] Large numbers of bipolar plates are needed for producing PEM fuelcells. In order to have the capability for manufacturing these numberscost-efficienty, the production process has to be capable of being runwith very short cycle time and a high level of automation. High latencyof the moulding composition is required to achieve this propertyprofile.

[0059] The examples below use the following components:

[0060] Epoxy resin 1: Epoxy cresol novolak with 4.35 val/kg epoxycontent

[0061] Epoxy resin 2: Bisphenol A diglycidyl ether with 2.2 val/kg epoxycontent

[0062] Hardener 1: Cresol novolak with 8.5 val/kg hydroxy group content

[0063] Catalyst 1: Microgel-amine salt prepared from methylmethacrylate, methacrylic acid, ethylene glycol dimethacrylate,trimethylolpropane trimethacrylate and 2,4-ethylmethylimidazole,prepared as in Example 11.5 of U.S. Pat. No. 5,994,475

[0064] EMI 2,4Ethylmethylimidazole

[0065] Graphite powder with an average particle diameter of 20 μm.

[0066] The compositions of the invention (see Example 1) have highlatency at temperatures of from 60 to 110° C. This is important, sincethe composition has to be heated to these temperatures forpreplastification during processing. At the same time, since the highfiller level in itself gives the composition high viscosity, any furtherincrease in viscosity has to be avoided in order to ensure sufficientflowability during mould filling. To simulate this behaviour duringprocessing of the moulding composition, the pellets of mouldingcompositions from Example 1 were conditioned for 3 and 6 minutes on acalender at two different temperature settings, and the changes inspiral flow path were compared. Table 1 clearly shows that while thereis from 30 to 40% fall-off from the initial flowability ofEMI-containing products, the flowability of which is relatively pooreven at the outset, the figure is only from 13 to 15% when microgelcatalysis is used. In practice this means that in the case ofconventionally accelerated moulding compositions even smallinterruptions in production have a significant effect on the quality ofthe bipolar plate. One of a number of disadvantages of mouldingcompositions with poor flowability is that they cannot be adequatelycompacted, and this can lead to loss of the gas-tight property of theplate, which is a prime requirement for reliable operation of the PEMfuel cell.

EXAMPLE 1 Flowability and Latency

[0067] The components given in Table 1 are mixed in a bead mill andhomogenized at from 90 to 110° C. on a calender. The flowability of theresultant pellets is then determined to ASTM D3123. TABLE 1 Component A(invention) B (comparison) a) Epoxy resin 1 13.37 13.37 a) Epoxy resin 28.69 8.69 b) Hardener 1 9.64 9.64 c) Catalyst 1 1.80 EMI (comparison)0.38 d) Graphite powder (20 μm) 65.0 66.42 d) Calcium stearate 0.50 0.50d) Hoechst OP 125 U wax 1.00 1.00 Total 100 100 Spiral flow 170° C.[inch/cm] with calender mixing for 3 minutes (rear/front roll) at90/100° C.  20.0/50.8 13.5/34.3 100/110° C.  18.0/45.7 9.75/24.8 for 6minutes (rear/front roll) at 90/100° C. 17.25/43.8   8/20.3 100/110° C. 15.5/39.4 6.75/17.1

EXAMPLE 2 Volume Resistivity

[0068] The effect of organosilanes on the Volume resistivity of thehardened mixtures is apparent when comparing compositions C and D. Thequantitative data for components in Table 2 are parts by weight. TABLE 2Component C D a) Epoxy resin 1 11.47 11.47 a) Epoxy resin 2 7.46 7.46 b)Hardener 1 8.27 8.27 c) Catalyst 1 1.80 1.80 d) Sikron B 300 powderedquartz 9.50 9.30 d) PPG EC10 5.00 5.00 d) Graphite powder (20 μm) 55.0055.00 d) γ-glycidyloxypropyltrimethoxysilane 0.20 d) Calcium stearate0.50 0.50 d) Hoechst OP 125 U wax 1.00 1.00   Volume resistivity [ohmcm] 0.305 0.218

[0069] The current state of the art requires volume resistivities of<0.1 ohm cm for the bipolar plate in order to avoid any adverse effecton the performance of the fuel cell. Measurements are typically made onround specimens (pressings) of diameter 3.5 cm and thickness at least1.5 cm. Since the method is greatly dependant on the area of contactbetween electrode and pressing, pressure is applied to the specimen instages of from 1 to 5 N/mm². The change in the values can be evaluatedas a criterion of quality of the surface of the pressing. If theintention is to eliminate the effect of unevenness on electricalconductivity, a flexible graphite mat may be placed between electrodeand pressing. FIG. 1 shows a diagram of an appropriate test assembly fordetermining volume resistivity. The reference numerals in the figureindicate: 1=holder, 2=load cell, 3=insulator, 4=graphite mat, 5=contact,6=test specimen, 7=voltmeter, 8=ammeter and 9=power source. Theprinciple of measurement used here is shown in FIG. 2 in the form of anelectrical circuit diagram of a 4-point conductivity measurement system.The reference numerals in FIG. 2 indicate: 1=power source, 2=testspecimen, 3=ammeter and 4=voltmeter.

[0070] Table 3 below shows that high graphite contents are needed toachieve these low resistances. The reduction in volume resistivity isunfortunately also associated with a fall-off in flowability. Thiseffect is also apparent from Table 3. The quantitative data for thecomponents in Table 3 are parts by weight. TABLE 3 Component E F G HEpoxy resin 1 15.48 13.37 11.26 9.15 Epoxy resin 2 10.06 8.69 7.32 5.95Hardener 1 11.16 9.64 8.12 6.60 Catalyst 1 1.80 1.80 1.80 1.80 Graphitepowder (20 μm), 60.00 65.00 70.00 75.00 Calcium stearate 0.50 0.50 0.500.50 Hoechst QP 125 U wax 1.00 1.00 1.00 1.00 Total 100.00 100.00 100.00100.00 Volume resistivity [ohm cm] 1.09 0.37 0.22 0.13 Spiral flow[inch] 29.5 17.5 11.0 5.0

[0071] Selection of graphite grades:

[0072] Suitable granulometry of component (d) can optimize spiralflowability and the conductivity of the formulation. Synthetic graphitesshould mainly be utilized here, since natural graphites comprise from 1to 3% of polyvalent cations which can become embedded in the membrane toadverse effect. Table 4 below shows the volume resistivities of theabove formulation G (Table 3) as a function of the grade of graphiteused. The data in brackets are the average particle diameter of thegraphite. TABLE 4 Spiral flow Volume resistivity (170° C.) Example Gradeof graphite [ohm cm] [inch/cm] G Synthetic (20 μm) 0.22 11.0/27.9 HSynthetic (50 μm) 0.14 23.0/58.4 I Synthetic (60 μm) 0.08 14.5/36.8 JSynthetic (100 μm) 0.12 22.0/55.9 K Synthetic (250 μm) 0.18 30.5/77.5 LSynthetic (500 μm) 0.16 31.0/78.7 M Natural flakes (50 μm) 0.1721.0/53.3 N Natural flakes (100 μm) 0.19 25.0/63.5 O Natural flakes (250μm) 0.10 34.0/86.4 P Natural flakes (300 μm) 0.16 31.0/78.7

[0073] The flowability of these formulations naturally increases withrising particle size of the graphite (see Table 4), but in parallel withthis there is also impairment of the surface quality of the hardenedmoulding compositions. The tendency of the moulding composition to formflash increases, and the requirement for post-treatment operationstherefore increases.

[0074] According to Table 4 the maximum electrical conductivity resultsfrom use of a synthetic grade of graphite with an average particle sizeof about 60 μm. A proportion of 73% by weight, based on the entirecomposition of components (a)+(b)+(c)+(d), proved here to be the idealcompromise between conductivity and flowability. If the flowability ofthis optimized formulation is now compared with an EMI-catalyzed variantof the same formulation, it is again found that the use of EMI givesinsufficient processability due to lack of adequate flowability(Examples S and T). To this end, the formulations were homogenized for 3and 4 minutes on a mixing calender with roll temperatures of 100/110° C.

[0075] The spiral flow paths for the EMI-catalyzed Example I halvedafter as little as 4 minutes, whereas only a small fall-off from 10 to 9inches (from 25.4 to 22.9 cm) is found for the microgel variants(Examples Q and R). See Table 5 below.

[0076] The selection of process parameters on the calender is such thatthe flow properties (spiral path) for the moulding composition aresimilar to those for an extrusion process. Satisfactory processingbecomes impossible if the spiral path after the mixing process is ≦5inches (12.7 cm). Depending on the latency behaviour of the composition,this value increases if the composition is subject to other heatingeffects (e.g. preplastification for the compression process) prior tothe actual application process. TABLE 5 Component Q (3 min) R (4 min) S(3 min) T (4 min) a) Epoxy resin 1 9.99 9.99 10.14 10.14 a) Epoxy resin2 6.50 6.50 6.59 6.59 b) Hardener 1 7.21 7.21 7.32 7.32 c) Catalyst 11.80 1.80 EMI (comparison) 0.39 0.39 d) Graphite 73.00 73.00 74.06 74.06powder (60 μm), synthetic d) Calcium stearate 0.50 0.50 0.50 0.50 d)Hoechst OP 125 U 1.00 1.00 1.00 1.00 wax Total 100 100 100 100 Volumeresistivity 0.05 0.05 0.05 0.05 [ohm cm] Spiral flow path 10/25.4 9/22.94/10.1 2/2.6 [inch/cm]

[0077] Properties of formulation Q are shown in Table 6 below: TABLE 6Property of pellet Plasticorder B value 160° C. [Nm] 1.2 Plasticorder ADvalue 160° C. [sec] 71 Plasticorder B value 120° C. [Nm] 4.6Plasticorder AD value 120° C. [sec] 285 Spiral flow II 170° C. [inch] 10Shore D 170° C. - demouldability 65; O.K. General properties Density[g/cm³] 1.78 Demouldability 1 mm plate O.K. Stability of 1 mm plate O.K.Shrinkage at 170° C. (%) 0.16 × 0.15 Mechanical properties Flexuralstrength [MPa] 51 Modulus of elasticity [GPa] 16 Elongation at break [%]0.35 Impact strength [kJ/m²] 1.5 Thermal properties Glass transitiontemperature [° C.] 164 Thermal conductivity [W/m · K] >15 Volumeresistivity One plate without skin [ohm · cm] 0.01-0.03 One plate withoriginal surface [ohm · cm] 0.05

1. Composition comprising (a) an epoxy resin, (b) a hardener for theepoxy resin, (c) a product of the reaction of a microgel containingcarboxylic acid groups and a nitrogen-containing base, and (d) anelectrically conducting filler combination comprising, based on thetotal amount of filler, at least 75% by weight of graphite. 2.Composition according to claim 1, comprising an epoxy phenol novolak oran epoxy cresol novolak as component (a).
 3. Composition according toclaim 1 or 2, in which the microgel in component (c) is a copolymer ofat least one unsaturated carboxylic acid and at least one polyfunctionalcrosslinker.
 4. Composition according to claim 3, in which theunsaturated carboxylic acid is acrylic acid or methacrylic acid. 5.Composition according to claim 3, in which the polyfunctionalcrosslinker is a polyfunctional acrylate or methacrylate of analiphatic, cycloaliphatic or aromatic polyol, an addition product ofacrylic acid or methacrylic acid and a polyglycidyl compound, anaddition product of acrylic acid or methacrylic acid and glycidylacrylate or methacrylate, an alkenyl acrylate or alkenyl methacrylate, adialkenylcyclohexane, or a dialkenylbenzene.
 6. Composition according toclaim 3, in which the polyfunctional crosslinker is selected fromethylene glycol diacrylate, ethylene glycol dimethacrylate, propyleneglycol diacrylate, propylene glycol dimethacrylate, 1,4-butanedioldiacrylate, 1,4-butanediol dimethacrylate, polyethylene glycoldiacrylate, polyethylene glycol dimethacrylate, polypropylene glycoldiacrylate, polypropylene glycol dimethacrylate,1,1,1-trimethylolpropane triacrylate,1,1,1-trimethylolpropanetrimethacrylate, bisphenol A diglycidyl etherdiacrylate, bisphenol A diglycidyl ether dimethacrylate, allyl acrylate,allyl methacrylate, divinylcyclohexane, and divinylbenzene. 7.Composition according to claim 1 or 2, in which the nitrogen-containingbase in component (c) is an amine, a polyamine or an imidazole. 8.Composition according to claim 7, in which the nitrogen-containing baseis 2-phenylimidazole, 2-isopropylimidazole, 2-dodecylimidazole,2-heptadecylimidazole, 2-ethylimidazole, or 2-ethyl-4-methylimidazole.9. Composition according to claim 1, in which the filler combination (d)comprises graphite powder with an average particle diameter of from 0.1to 500 μm, preferably from 1 to 300 μm, more preferably from 10 to 250μm, with particular preference from 50 to 100 μm.
 10. Compositionaccording to claim 1, in which the filler combination (d) comprisesgraphite powder in the form of synthetic graphite.
 11. Compositionaccording to claim 1, comprising from 0.1 to 25 parts by weight ofcomponent (c), based on 100 parts by weight of component (a). 12.Composition according to claim 1, comprising from 50 to 90% by weight,preferably from 70 to 85% by weight, of component (d), based on theentire composition (a)+(b)+(c)+(d).
 13. Composition according to claim1, also comprising an organosilane.
 14. Electrically conductive materialproduced by hardening a composition according to claim
 1. 15. Use of acomposition according to claim 1 for producing bipolar plates.